SPINE Volume 30, Number 11, pp E311–E314 ©2005, Lippincott Williams & Wilkins, Inc. Bilateral Pedicle Fractures Following Anterior Dislocation of the Polyethylene Inlay of a ProDisc® Artificial Disc Replacement A Case Report of an Unusual Complication Philip Mathew, MRCS,* Mark Blackman, FRCS,* Sridhar Redla, MD, FRCR,† and Ahmed A. Hussein, FRCS* Study Design. An unusual complication resulting from an artificial disc replacement for lumbar degenerative disc disease and its treatment are reported Objective. To describe the clinical circumstance, radio- logic findings, treatment, and outcome of bilateral pedicle fractures associated with dislocation of the polyethylene inlay of a ProDisc® replacement at L5/S1 level. Summary of Background Data. To the authors’ knowl- edge, no published reports in the English literature have described bilateral pedicle fractures following a single level artificial lumbar total disc replacement. Methods. A 30-year-old male underwent a ProDisc® total disc replacement at L5/S1 level for discogenic pain. Six-week postoperative assessment showed improve- ment in the visual analog and Oswestry scores. Assess- ment at 18 weeks postoperatively for acute pain revealed an anterior slip of the superior plate component, and computerized tomography showed bilateral pedicle frac- tures of the fifth lumbar vertebra. At surgery, the poly insert was found to have dislocated anteriorly. A salvage interbody fusion was then performed using the stand- alone anterior lumbar interbody fusion cage. Results. The most recent review confirmed radiologic evidence of fusion with improvement in the subjective evaluation scores Conclusions. We hypothesize that the current implant design in which the contribution to lordosis angle is purely from the superior component may be responsible for the reported complication. We suggest that dividing the contribution equally between both endplates might increase the stability, and this has been discussed with the manufacturers. Key words: ProDisc®, total disc replacement, pedicle fracture, complication, stand-alone anterior lumbar inter- body fusion. Spine 2005;30:E311–E314 A total of 70% to 80% of the population of the Western world has mechanical low back pain at one time or the other. 1 Intervertebral disc degeneration is implicated as a causative factor in mechanical back pain. 2 The conven- tional, established treatment for this disorder is disc re- moval and interbody fusion. 3–5 However, total disc re- placement is fast evolving as a suitable alternative because it aims to restore or preserve the natural biome- chanics of the intervertebral segment and reduce further degeneration at adjacent segments. 6,7 With advance- ments in implant design and increased use, more compli- cations are now being reported. In this article, we report an unusual complication of bilateral pedicle fractures of the fifth lumbar vertebra following anterior dislocation of the polyethylene inlay of a ProDisc® II (Synthes Inc., West Chester, PA) artifi- cial disc replacement for mono-segmental (L5/S1) degen- erative disc disease in a 35-year-old male carpenter. To the authors’ knowledge, no published reports in the En- glish literature have described bilateral pedicle fractures following a single level artificial disc replacement. Case Report A 30-year-old male carpenter with a 10-year history of low back pain presented to the spinal clinic with exacer- bation of symptoms. He complained of constant lower back pain since being involved in a traffic accident at the age of 16 years and a recent history of intermittent radi- ation down the right side (visual analog scale [VAS] score 6 –7 out of 10 at its worst). He had been unemployed for the past year and mentioned the pain in his back to be the cause. No other significant medical history of note ex- cept a right inguinal hernia repair when he was a child. Clinical examination revealed signs of right-sided L5 and S1 nerve root irritation without any neurologic com- promise, and some restriction of spinal movements. He was initially treated with physiotherapy and then with a caudal epidural and facet joint injections without any success. At the 12-month clinic review, his symptoms had worsened (Oswestry score 8 60%, back pain VAS score 9 of 10, back-to-leg pain ratio 8:2, walking dis- tance of approximately a quarter of a mile), and, clini- cally, there was significant limitation of spinal move- ment, although muscle tone and power, sensation, reflexes, and bowel and bladder function were all nor- mal. Plain radiographs showed the loss of intervertebral disc height at L5/S1 level. Magnetic resonance imaging showed the loss of disc signal at L5/S1, Modic type 2 changes in the lower endplate and a paracentral right sided disc prolapse with significant compression of S1 From the Departments of *Orthopaedics and †Radiology, Princess Alexandra Hospital, Harlow, United Kingdom. Acknowledgment date: May 20, 2004. First revision date: September 24, 2004. Acceptance date: September 29, 2004. The legal regulatory status of the device(s)/drug(s) that is/are the sub- ject of this manuscript is not applicable in my country. No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript. Address correspondence and reprint requests to Philip Mathew, MRCS, Trauma Fellow, Department of Orthopaedics, Princess Alex- andra Hospital, Hamstel Road, Harlow CM20 1QX, United Kingdom; E-mail: philip.mathew@virgin.net E311